Growth and colour development of some surface ripening bacteria with Debaryomyces hansenii on aseptic cheese curd.

The growth of five bacteria isolated from red-smear cheeses, Brevibacterium aurantiacum, Corynebacterium casei, Corynebacterium variabile, Microbacterium gubbeenense and Staphylococcus saprophyticus in mixed cultures with Debaryomyces hansenii on aseptic model cheese curd at 10 and 14 degrees C was investigated. At both temperatures, C. casei and Micro. gubbeenense had a longer lag phase than C. variabile, Brevi. aurantiacum and Staph. saprophyticus. In all cultures, lactose was utilised first and was consumed more rapidly at 14 degrees C than at 10 degrees C, i.e., 6 d at 14 degrees C and 10 d at 10 degrees C. This utilisation coincided with the exponential growth of Deb. hansenii on the cheese surface. Lactate was also used as a carbon source and was totally consumed after 21 d at 14 degrees C and approximately 90% was consumed after 21 d at 10 degrees C regardless of the ripening culture. Small differences (<0.5 pH unit) in the surface-pH during ripening were noticeable between ripening cultures. Differences in the colour development of the mixed cultures with the yeast control were only noticeable after 15 d for Brevi. aurantiacum and after 21 d for the other bacteria. Regardless of the organisms tested, colour development and colour intensity were also greater at 14 degrees C than at 10 degrees C. This study has provided useful information on the growth and contribution to colour development of these bacteria on cheese.

Deacidification by Debaryomyces hansenii of smear soft cheeses ripened under controlled conditions: relative humidity and temperature influences.

Model smear soft cheeses were prepared from pasteurized milk inoculated with Debaryomyces hansenii (304, GMPA) and Brevibacterium aurantiacum (ATCC 9175) under aseptic conditions. Debaryomyces hansenii growth and curd deacidification were studied in relation to ripening chamber temperature and relative humidity (RH). A total of 9 descriptors, mainly based on kinetic data, were defined to represent D. hansenii growth (2 descriptors), cheese deacidification (5 descriptors), and cheese ripening (2 descriptors). Regardless of the temperature, when the RH was 85%, D. hansenii growth was inhibited due to limitation of carbon substrate diffusions; consequently, cheese deacidification did not take place. Debaryomyces hansenii growth was most prolific when the temperature was 16 degrees C, and the RH was 95%. Kinetic descriptors of lactate consumption and pH increase were maximal at 16 degrees C and 100% RH. Under these 2 ripening conditions, on d 14 (packaging) the creamy underrind represented a third of the cheese; however, at the end of ripening (d 42), cheese was too liquid to be sold. Statistical analysis showed that the best ripening conditions to achieve an optimum between deacidification and appearance of cheeses (thickness of the creamy underrind) were 12 degrees C and 95 +/- 1% RH.

Behavior of Brevibacterium linens and Debaryomyces hansenii as ripening flora in controlled production of smear soft cheese from reconstituted milk: growth and substrate consumption dairy foods.

Experimental cheeses inoculated with Debaryomyces hansenii and Brevibacterium linens were ripened for 76 d under aseptic conditions. Triplicate cheese-making trials were similar as a result of efficient control of the atmosphere. In all trials, D. hansenii grew rapidly during the first 2 d and then slowed, but growth remained exponential until d 10 (generation time around 70 h). Total cell counts were higher than the number of viable cells, and after 10 d they remained around 3 x 10(9) yeast/g of DM. This difference resulted from the nonviability of a fraction of D. hansenii. After d 15, the pH of the rind was close to 7, and B. linens grew exponentially until d 25 (generation time around 70 h). The growth rate subsequently decreased but remained exponential (generation time around 21 d). Cell counts of D. hansenii and B. linens were correlated with the environmental technical conditions. Total D. hansenii counts were also correlated with total B. linens counts. Viable B. linens counts were related to rind lactate, and total counts depended on rind pH, internal lactate, and D. hansenii viable counts. The internal pH of the cheese depended on lactate concentrations, whereas surface pH was related to internal lactose, temperature, and relative humidity. These results suggest a determining role of the diffusion of the carbon sources in the ripening of smear soft cheese.

Behavior of Brevibacterium linens and Debaryomyces hansenii as ripening flora in controlled production of soft smear cheese from reconstituted milk: protein degradation.

Model smear soft cheeses, prepared with Debaryomyces hansenii and Brevibacterium linens as ripening starters, were ripened under aseptic conditions. Results of the cheese-making trials, in triplicate, were similar and showed similar patterns of protein degradation. In all of the trials, the acid-soluble nitrogen and nonprotein nitrogen (NPN) indexes and NH3 concentrations of the rind were low until d 10. The acid-soluble nitrogen and NPN of the rind then increased to 100 and 18% of total nitrogen, respectively, at d 76. The NH3 concentrations remained low until d 24 and increased until d 70, reaching about 1.8 g of NH3/kg of DM, and then remained constant. The acid-soluble nitrogen and NPN indexes and NH3 concentrations in the inner cheese mass were lower than in the rind. They showed the same evolution, reaching about 18% for acid-soluble nitrogen, 10% for NPN, and 1.5 g of NH3/kg of DM. It was shown that the inner cheese pH and populations of D. hansenii and B. linens have an effect on proteolysis. Viable cell counts of D. hansenii and B. linens were correlated with the environmental conditions and with proteolytic products. The determining role of carbon source and NH3 diffusions on the cheese ripening process were confirmed.